Abstract:

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Equal channel angular extrusion (ECAE) was performed on as-cast ZW1101 (Mg-11wt%Zn- 0.9wt%Y) Mg alloy containing quasicrystallines. The grain size of α-Mg was effectively refined, and coarse eutectic quasicrystalline phases were broken and dispersed in the alloy by ECAE. The alloy processed by ECAE exhibited a good combination of high strength and high ductility, which is due to the grain refinement and fine dispersed quasicrystallines in the alloy.

Abstract: Superplastic forming provides a good way for Ti alloys which are usually difficult to
be deformed. Ti75 alloy with a nominal composition of Ti-3Al-2Mo-2Zr is a newly developed corrosion resistant alloy, with a middle strength and high toughness. In the present paper, superplastic behavior of the alloy was investigated, the microstructural evolution in superplastic deformation was observed and the superplastic deformation mechanisms were analyzed. The results showed that the strain rate sensitivity, m, of the Ti75 alloy was larger than 0.3 and the strain was over 2.0 without surface cracking at 800°C and 5×10-4s-1 in compressive testing.
During the first stage of superplastic deformation, a phase grains became equiaxed, fine and homogeneous due to the recrystallization in a phase and diffusion in b phase. Newly formed equiaxed a grains then could slide and rotate, exhibiting superplastic features. The stress concentration caused by grain sliding of a grains could be released by slip and diffusion in b phase between the a phase grains, which acted as accommodation mechanisms.

Abstract: Warm compression tests of AZ31 Mg alloy were carried out at five temperatures in
30°C intervals from 210°C to 330°C. The samples of different thickness which were machined
from as-cast and pre-strained AZ31 billets were compressed into thickness 1mm and then cooled in
the air to room temperature. The microstructural evolution of AZ31 Mg alloy was investigated
during warm compression forming. The results show that all the samples have undergone a
microstructure changes to different scales in the range investigated. The twinning is the
predominant deformation mechanism for magnesium alloys at moderate temperatures and its
occurrence is dependent on temperature and strain. Microstructural evaluation indicates that the
mean size of the recrystallised grains decreases with increasing effective strain and temperature
because of sufficient dynamic recrystallization. The original grain has significant influence on
microstructural evolution during warm forming.

Abstract: Rheocasting of alloys A206 and A201 was investigated in this study. Conical bars with
different silver contents were produced using CSIR rheoprocess technology, together with high
pressure die casting. The results showed that addition of Ag to alloy A206 increased the mechanical
properties of the alloy. However, the addition of Ag also resulted in Cu-rich phases to precipitate at
the grain boundaries of the as-cast material. The solution treatment used in this study was unable to
dissolve all of this phase, especially in the 1.12%Ag-containing alloy. This resulted in slightly
decreased mechanical properties compared to the 0.63%Ag-containing alloy. The T6 mechanical
properties (strength and elongation) obtained in this study for rheocast A206 and A201 are better
than those reported for permanent mould castings of alloy A206 and A201.

Abstract: The effect of Cd and Sb addition on the microstructural and mechanical properties of as-cast AZ31 alloys was investigated and compared. The results indicate that the difference of Sb and Cd in the microstructure and mechanical properties of as-cast AZ31 magnesium alloy is significant. Addition of 0.15%Sb (mass fraction) to AZ31 alloy can refine the matrix and β-Mg17Al12 phase but not form a new phase Mg3Sb2. Oppositely, by addition of 0.3-0.7% Cd to AZ31 alloy, Cd was dissolved into the AZ31 alloy, the phase composition did not change but was refined also. Accordingly, the Cd-refined AZ31 alloy exhibits higher tensile and impact toughness and Brinell hardness properties than the Sb- refined one. The difference of Sb and Cd in the mechanical properties is possibly related to the solid solution of Cd into the matrix and formation of Mg3Sb2 which has the same close-packed hexagonal structure as α-Mg.

Abstract: Bulk nanostructured (grain sizes in the range of 50-200nm) and ultrafine structured (grain sizes in the range of 100-500nm) -TiAl based alloys with compositions Ti-47Al (in at%) and Ti–45Al–2Cr–2Nb–1B–0.5Ta (in at%), respectively, have been produced using a combination of high energy mechanical milling of mixtures of elemental powders and hot isostatic pressing at 800 and 1000oC respectively, and the microstructures of the samples have been characterised. At room temperature, the HIPed samples fractured prematurely at tensile stresses in the range of 200-300MPa and showed no ductility, very likely due to the relative high oxygen content (0.6wt%) in the samples and very low tolerance of TiAl based alloys on dissolved oxygen. At 800oC, the HIPed samples showed a yield strength in the range of 55-70MPa, a tensile strength in the range of 60-80MPa, a large amount of elongation to fracturing around 100% and clear strain softening. Examination of the fractured tensile test specimens at room temperature and 800oC showed that the level of the consolidation was fairly high, but the HIPed samples do contain a small fraction of interparticle boundaries with weak atomic bonding. The fracture of the HIPed samples in tensile testing at room temperature and 800oC, respectively, is predominately intergranular, and the large amount of plastic deformation prior to fracture at 800oC is achieved mainly through grain boundary sliding in conjunction with dislocation gliding, in agreement with the deformation mechanisms of nanostructured and ultrafine structured alloys generally agreed by researchers.